Method of preventing infiltration in wells



Patented Mar. 28, 1939 METHOD OF PREVENTING INFILTRATION IN WELLS John J. Grebe, Midland, Mich" assignor to The Dow Chemical Company, Midland, Mich.', a corporation of Michigan No Drawing. Application June 24,1987, Serial No. 150,131

'iClaims.

The invention relates to methods of shutting off. water infiltration in oil and gas wells, wherein a solution of a reagent is introduced-into the well formation to produce a precipitate by reacting with the water or with the dissolved constituents thereof. It more particularly concerns an improved method of forming a plugging deposit in the formation effectively reducing its permeability to the passage of water without materially reducing its permeability to oil.

Methods heretofore proposed for shutting off water in oil or gas wells, which depend upon injecting into the water-producing stratum a solution containing an agent forming a precipitate with the water, often fail to give satisfactory results. In some cases the precipitates are unable to withstand the strong water pressure often encountered in deep wells. Furthermore, the

agents heretofore proposed can be injected into the formation only for a relatively short distance, owing to premature precipitation.

It has been proposed to introduce a solution of a water-soluble soap into water-bearing strata of deep wells to reduce water infiltration, since the waters therein are invariably hard and produce water-insolubleprecipitates with soap solutions.- I have found that soap solutions are not always effective for the purpose, particularly in deep wells where the water pressure is often very great.- Tests made indicate that it is usually dimcult to obtain adequate penetration of the solution into the formation, due to the fact that it reacts quite rapidly with the calcium or magnesium salts present in the ground water pro- I ducing a precipitate hindering the further penetration of the solution. As a result the solution travels but a relatively short distance before precipitation prevents further penetratiomunless excessive injection pressures are applied. The precipitate so produced, I have found, does not resist back pressures which are much greater than the injection pressure. On releasing the injection pressure, therefore, the ground waters return and in time may wash theprecipitate out of the formation. v

I have found that by including an alkalimetal phosphate in the soap solution the disadvantages incident to the use of soap solutions are substantially overcome. Introduction into the formation of a solution containing both a water-soluble soap and an alkali-metal phosphate not only can be accomplished readily without dlillculty from premature precipitation, but also usually without material risk of hindering the flow'ofoil to the well; because the solution is substantially inert to oil. When the solution reacts with the ground waters, insoluble phosphate is precipitated out along with the insoluble soap, producing a more rigid plugging deposit than that obtained with soap solutions alone.

In carrying out the invention a solution of an alkali-metal phosphate and a soluble soap is prepared, preferably by mixing an aqueous solution of a phosphate with an aqueous solution of a soap, or many other convenient manner, as by 10 dissolving the respective ingredients in water. A considerable variation in the concentration of either the soap or the phosphate in the solution employed is allowable. For example, a solution containing from 20 to 50 per centv of a water- 15 soluble soap and from 2 to 25 per cent of an alkali-metal phosphate has been found satisfactory, the proportlon of soap being preferably in excess of that of the phosphate. A generally effective solution is one comprising approximately 40 per cent by weight of the potassium soap of cocoanut oil and approximately 20 per cent by weight of trlsodium phosphate, the balance being water. Other common soaps, e. g. sodium stearate, sodium palmitate, may be substituted 2 for the soap mentioned.

Before introducing the solution into the well it isgenerally desirable to remove any brine from the bore of the well and to flush it out with fresh water. Some fresh water or oil may be 30 advantageously introduced into the well ahead of the solution. The solution is introduced into the well and pressure may be applied to it to insure forcing it into the formation. This may be done by introducing a quantity of oil into the 5 well after the solution producing a hydrostatic head forcing the solution out of the well bore into the formation. A pressure in excess of that in the water-bearing formation is required. The pressure is maintained upon the solution to per 40 mit the reagent to react with the ground water or salts therein to form awater-insoluble precipitate or deposit in the water-bearing pores. After a sufliclent period of time, e. g. from 24 to .48 hours, the pressure is released, and any excess 45 of the solution may be removed by pumping or bailing.

The introduction into a formation containing brine or hard water of a solution of the type described has the advantage of not developing 5o clogging deposits as rapidly as a solution containing soap alone. This is decidedly advantageous in aiding penetration of the solution deeply into the formation before reaction is complete. The solution forms water-insoluble 56 deposits in the formation not as readily displaceable by water or brine as those produced by solutions containing soap alone. The plugging action of the solution is selective since it is substantially inert to oil and may be flushed out of oil-bearing passages by the flow of oil when the injection pressure is released.

Other modes of applying the principle of my invention may be employed instead of those explained, change being made as regards the method herein disclosed, provided the step stated by any of the following claims or the equivalent of such stated step be employed.

I therefore particularly point out and. distinctly claim as my. invention:

1. In a method of treating water-bearing formations adjacent the bore of an oil or gas well, the step which consists in introducing into the well a treating solution comprising an alkalimetal phosphate and a water-soluble soap.

2. In a method 01' treating water-bearing tormations adjacent the bore of an oil or gas well, the step which consists in introducing into the well an aqueous treating solution comprising an alkali-metal phosphate and a water-soluble soap, the proportion of soap in the solution being in excess of that of the phosphate.

3. In a method of treating water-bearing formations adjacent the bore of an oil or gas well, the step which consists in introducing into the well an aqueous treating solution comprising trisodium phosphate and a water-soluble soap.

4. In a method of treating water-bearing formations adjacent the boreot an oil or gas well, the step which consists in introducing into the well an aqueous treating solution comprising approximately 2-25 per cent by weight of alkalimetal phosphate and approximately 20-50 per cent by weight of a water-soluble soap, the soap being in excess of the phosphate.

5. In a method of treating water-bearing earth or rockformations adjacent the bore 'of an oil or gas well, the step which consists in introducing into the well an aqueous treating solution comprising approximately 20 per cent by weight trisodium phosphate and approximately 40 per cent by weight of a water-soluble soap.

6. In a method of treating water-bearing formations adiacent the bore of an oil or gas well, the step which consists in introducing into the well under a pressure in excess of that in the water-bearing formation a treating solution comprising an alkali-metal phosphate and a watersoluble soap.

7. In a method of trgating water-bearing formations adjacent the bore of an oil or gas well, the steps which consist in introducing into the well under a pressure in excess of that in the water-bearing formation a treating solution comprising an alkali-metal phosphate, a water-soluble soap and introducing a quantity of oil to produce a hydrostatic head forcing the treating solution out of the well bore.

JOHN J. GREBE. 

